The deployment of stents at a stenting site within a human or animal body requires careful handling of the stent delivery system to be used for deploying the stent. Exact positioning of the stent at the site of the stenosis prior to and during deployment is essential. The accuracy with which the stent can be deployed with respect to the occlusion inside the body lumen, as well as the skills of the surgeon in controlling the stent delivery system, will having an impact on the outcome of the operation.
Normally, a guidewire is used, to advance a stent delivery system containing the stent to be deployed into the body to the site of the stenosis. Once the distal end of the delivery system has reached the stenting site and the stent to be released is correctly located, the stent is released. To deploy a self-expanding stent it is known to gradually withdraw an outer sheath (otherwise called sleeve) holding the stent in a radially compressed configuration and thereby allow the stent to radially expand and to anchor itself inside the body lumen. In commercially available delivery systems, the stent is prevented by an inner catheter from moving proximally with the sleeve as it retreats proximally, and is held in a radially compressed state by a co-axially disposed outer sheath or sleeve enclosing the stent and the inner catheter. The relative axial positions of the inner catheter and the outer sleeve are varied by manipulation of the delivery system.
Since the stent as well as the stenosis are not directly visible to the surgeon performing the operation, the stent deployment procedure requires a visualization procedure, usually the injection of a radiopaque fluid, in order to visualize the location of the stent inside the body lumen. The fluid is injected into an annular cavity between the inner catheter and the outer sheath. The position of the stent as well as the location of the stenosis itself can then be monitored from outside the patient's body by using X-ray imaging machines showing the images of radiopaque marker rings on the distal end of the delivery system and a reduced intensity image corresponding to the constricted volume of radiopaque fluid through the occluded site. This allows the surgeon/radiologist to find the location of the stenosis and place the stent with sufficient accuracy.
During the course of the delivery procedure, the radially compressed stent is held axially at a fixed position by a pusher surface of the inner catheter, which typically abuts the proximal end of the stent inside the outer sheath of the delivery system. The proximal movement of the outer sheath to release the stent exerts a proximally directed force onto the stent which urges the stent to move in the same way. The surgeon has to counteract this tendency of the stent to move proximally by applying an adequate, distally-directed force onto the pusher element in order to off-set the opposing forces and to thereby keep the position of the stent fixed.
Typically, the stent is mounted into the delivery system at a manufacturing site. Then, the entire assembly is sterilized and air-tightly packed in a specially designed sealed enclosure. During sterilization and packaging, there is always the risk that the co-axial components of the assembly might move so that the outer sheath may be displaced with respect to the inner catheter. Consequently, the position of the stent might be changed during these steps prior to its placement.
Therefore, it would be desirable to have a delivery system with a fluid injection port which is protected against inadvertent or premature movement of the outer sheath relative to the stent but is still simple to use and economical to manufacture.
Some delivery devices are particularly applicable to the release into the body of a self-expanding stent, such as one made from nickel-titanium shape memory alloy. Self-expanding stents usually have a basically cylindrical form prior to deployment and it is conventional to deploy these stents with a system having two components. One of these components is a sleeve or sheath which surrounds the stent and constrains it to a radially compact disposition. The other component is a so-called “pusher” which is located inside the constraining sleeve and bears against a surface of the stent. Deployment of the stent is then accomplished by proximal withdrawal of the sleeve relative to the pusher. The pusher maintains the stent in a location relative to the target site of surgery. The proximal withdrawal of the sleeve progressively releases the stent, first at its distal end and then progressively proximally along the length of the stent until, when the distal end of the sleeve is proximal of the proximal end of the stent cylinder, the stent is fully deployed. At this point, the sleeve and pusher delivery system can be withdrawn proximally out of the body, leaving the stent, expanded, in the desired location. An early disclosure of such a system can be found in Gianturco U.S. Pat. No. 4,580,568.
Radiopaque markers on the stent delivery system (sometimes supplemented by markers on the stent itself) are used to enable radiologists to visualize the location of the stent in the body. Furthermore, the stent delivery system is used as a conduit for filling the bodily lumen to be stented with radiopaque fluid, to enable the radiologist to pinpoint the location of the stenosis or other surgical site where the stent is to be placed. It is then the task of the medical practitioner performing the stenting procedure to bring the radiopaque stent markers into the desired relationship with the site of surgery as indicated by the radiopaque fluid.
There continue to be difficulties for medical practitioners in placing the stent exactly as required. What has been needed now for many years is a delivery system which a medical practitioner can manipulate manually with enough precision to bring the stent reliably into the desired location relative to the surgical site. It will be appreciated that stent delivery systems are commonly of a length around 130 cm—such as when delivered by a Seldinger technique—so the medical practitioner is to some extent handicapped by having to work at considerable distance from the stent itself.
Stents come in many different lengths. However, for all but the shortest stent length, there are, to the knowledge of the present inventor, two phases in any self-expanding stent deployment sequence.
In a first phase, initial proximal withdrawal of the surrounding sleeve releases the distal end of the stent so that this part of the stent length begins to make contact with the bodily lumen which defines the site of surgery. This first phase is characterized in that the stent is still bound to the delivery system and not to the bodily lumen. However, at the end of the first phase, enough of the length of the stent has expanded into contact with the lumen wall to fix the position of the stent relative to the lumen wall. At this point, the stent is bound to both the delivery system and the bodily lumen wall, so that any axial movement of the delivery system relative to the bodily lumen is liable to cause injury to the lumen wall.
The second phase of stent deployment is what follows thereafter, namely, the remainder of the proximal movement of the sheath to release the remaining length of the stent into the bodily lumen. It will be appreciated that any axial stress on the deployed portion of the length of the stent during deployment will transmit to axial stress on that part of the bodily lumen which is in binding engagement with the stent, with the consequence that lumen wall supported by the stent remains in tension and under stress after the stent has been fully deployed. This unwanted axial stress in the bodily tissue could be severely deleterious to the patient in one way or another and is normally to be avoided.
There are proposals in the patent literature for placement of self-expanding stents by progressive distal advancement of a surrounding sheath, to release the stent, proximal end first, terminating at the distal end of the stent. It will be appreciated that this is possible because the radial expansion of the stent opens up a lumen big enough for proximal withdrawal of the sheath from a position distal of the expanded stent. The discussion of axial stresses can be applied, mutatis mutandis, to these configurations proposed in the patent literature, in which the proximal end of the stent is deployed first.
Also previously proposed are combinations of constraining sheaths which withdraw from the stent simultaneously proximally and distally, from a starting point intermediate the ends of the stent, in order to deploy the stent first from a mid part of its length, and terminating with deployment of both the proximal and distal ends of the stent. Even in such systems, the concerns about axial stresses still apply.
For a disclosure within the state of the art of a system which distinguishes between the initial phase of stent deployment and the subsequent phase in which the remainder of the length is deployed, reference is made to WO 99/04728. In this disclosure, it is proposed to use a stent delivery system which is characterized by an initial mechanical advantage for the initial stages of stent deployment, which is large enough to overcome static frictional forces between the stent and the surrounding sheath and to allow the initial part of the length of the stent to be deployed slowly and precisely. Once the sheath has begun sliding over the stent length, and an end of the stent has expanded to engage the surrounding luminal wall, a different and lower mechanical advantage is activated, to withdraw the sheath proximally at a rate more rapid than that characteristic of the initial phase of stent deployment.
It is the experience of the present inventor that individual medical practitioners have developed their own preferred techniques for precise deployment of stents. Looking at the proximal end of the stent delivery system, with the actuator which the practitioner actually handles during the stent deployment procedure, the state of the art offers various configurations and the individual practitioners select from these possibilities the actuators which fit their particular manual skills best.
WO 99/04728, mentioned above, offers the practitioner a knurled rotary actuation element whereas WO 00/18330, DE-A-44 20142 and WO 98/23241 are examples of pistol grip devices in which deployment is accomplished by a form of squeeze handle or trigger. See EP-A-747 021 and U.S. Pat. No. 5,433,723 for other examples of rotary stent release devices.
Another approach to the accomplishment of a controlled release of a self-expanding stent can be found in U.S. Pat. No. 5,683,451, the approach relying on so-called runners which lie between the stent and a surrounding sheath. At the proximal end of the delivery system, a follower receives a hub at the proximal end of the surrounding sheath and rotation of a handle causes rotation of a threaded shaft, along which the follower advances, to carry the proximal hub of the sheath in a proximal direction to release the stent.